1. Field of the Invention
The present invention relates to a hinge device suitable for opening and closing a document press-contacting plate of a copying machine, a printing machine, and the like.
2. Description of the Related Art
In the conventional copying machines, printing machines, and the like, a document press-contacting plate with a built-in automatic document feeder, which is relatively heavy in weight has been widely used, and for opening and closing such document press-contacting plates, such a hinge device as shown in the Japanese Patent Laid-open No. Hei11-174597 is publicly known.
The conventionally structured hinge device (a device for opening and closing a document press-contacting plate) comprises: an attachment member attached on an apparatus body side; a support member supporting a document press-contacting plate which is pivotally attached to the attachment member through a hinge pin; a pair of spring cases also serving as spring reception members pivotally supported by the supporting member side and the attachment member in a manner to be swingable and mutually compressible; compression springs elastically provided between the pair of spring cases; and a damper set inside the compression springs and fixably provided in either one of the spring cases.
Further, as a means to adjust rotation torque of the supporting member by changing the elastic force of the compression springs, the one shown in the Japanese Utility-model Publication No. Hei5-8599, for example, in which a spring reception seat is provided on the base portion of one of the spring cases by using an adjusting screw in a manner to be axially movable is well known.
When the two publicly known arts described above are combined, a structure in which the base portion of the damper is fixed on the spring reception seat is conceived. However, with such a structure, a torque adjustment requires the distance between the confronting spring cases to be changed by moving the spring reception seat in the axial direction. This causes a problem where, upon a closing of a document press-contacting plate, the closure angle of the document press-contacting plate changes at and from which the damper arranged in the compression springs begins to operate.